World Housing Encyclopedia an Encyclopedia of Housing Construction in

Seismically Active Areas of the World

an initiative of Earthquake Engineering Research Institute (EERI) and

International Association for Earthquake Engineering (IAEE)

HOUSING REPORT Reinforced concrete buildings in Pakistan

Report # 159

Report Date 07-07-2010

Country PAKISTAN

Housing Type RC Moment Frame Building

Housing Sub-Type RC Moment Frame Building : Designed for seismic effects, with URM infills

Author(s) Yasir Irfan Badrashi, Qaisar Ali, Mohammad Ashraf

Reviewer(s) Dominik Lang

Important This encyclopedia contains information contributed by various earthquake engineering professionalsaround the world. All opinions, findings, conclusions & recommendations expressed herein are those of thevarious participants, and do not necessarily reflect the views of the Earthquake Engineering ResearchInstitute, the International Association for Earthquake Engineering, the Engineering InformationFoundation, John A. Martin & Associates, Inc. or the participants' organizations.

Summary

This report addresses reinforced-concrete buildings in Pakistan. Due to the rapid urbanizationin Pakistan in the recent past and consequently the scarcity and inflated cost of land in themajor cities, builders have been forced to resort to the construction of reinforced-concretebuildings both for commercial and residential purposes. It is estimated that reinforced-concrete buildings constitute 10 to 15% of the total building stock in the major cities of

Pakistan and this percentage is on the rise. However, construction of reinforced concretebuildings in Pakistan is still in nascent stage with construction procedures lacking compliancewith the established construction procedures. This report is based on survey of the buildingstock of 5 major cities in Pakistan and hence provides a realistic picture of construction ofreinforced-concrete buildings in Pakistan. The statistics provided in this report are based onpersonal observation of the authors as well as opinion of professionals working in theconstruction industry who were interviewed in the course of this survey.

1. General InformationBuildings of this construction type can be found in the urban areas of the major cities being the hub of this kind ofconstruction. Construction of reinforced-concrete buildings is on the rise in the cities of Peshawar, Islamabad, Lahore,Faisalabad and Karachi. This is mainly due to the better economic conditions in these cities, higher population as wellas high land costs. In the sub-urban cities, reinforced concrete buildings are constructed, however, their primaryfunction is to accommodate commercial facilities and they are not usually taller than 3 to 4 stories. Percentage ofreinforced-concrete buildings in the sub-urban areas is low (1 to 2% of the total building stock). This type of housingconstruction is commonly found in urban areas.

Reinforced concrete buildings are most commonly constructed in the urban regions of Pakistan. However, it is notuncommon to see reinforced-concrete structures in the sub-urban cities too, though in the majority of the cases, theiruse is confined to commercial purposes (hotels, shopping centers etc.). Major cities of Pakistan have seen rise in theconstruction of reinforced concrete frame structures in the past two decades. This rise in construction of reinforced-concrete structures can be attributed to the improvement in the economic conditions of the people as well as awarenessof the fact that these are a better alternative as compared to traditional unreinforced brick masonry load bearingstructures in many aspects, particularly in performance during earthquakes. Since there has been a population burst inPakistan in the past couple of decades, the land prices have risen appreciably. This has forced builders to adapt toreinforced concrete structures as residential units in addition to their previous role of accommodating commercialfacilities. In the other major cities, like Islamabad and Lahore etc., about 10% to 15% buildings are being constructedas reinforced concrete, though commercial and public buildings like plazas, hotels, hospitals, educational institutionsetc. constitute the major portion of this percentage. Reinforced concrete structures in these cities are usually low-to-midrise (3 to 8 stories) however in exceptional cases, reinforced-concrete buildings as tall as 10 to 15 stories are beingconstructed nowadays. In the relatively less developed cities like Peshawar, Quetta, Faisalabad etc. the ratio ofreinforced-concrete buildings of the overall building stock may be lesser, a careful estimate being approximately 5% andthey are primarily used for housing commercial and public facilities. Reinforced-concrete buildings in these cities arealso low-to-mid rise (3 to 8 stories) with a story height of 3 to 3.35 meters. In Karachi, the percentage of reinforced-concrete structures amongst the total building stock is higher (15 to 20% of the total building stock). Usuallyreinforced-concrete buildings in Karachi are from 15 to 20 stories tall with a story height of 3 to 3.35 meters. Thishigher percentage of reinforced-concrete buildings in Karachi may be attributed to the high population and the factthat Karachi is the business hub for economic activities.

This construction type has been in practice for less than 25 years.

Currently, this type of construction is being built. Reinforced-concrete buildings have been constructed in Pakistan formore than 25 years but their percentage has been very low during that time. In the recent past, construction ofreinforced concrete buildings has been on the rise, especially in the national capital and the provincial capitals.

2. Architectura l Aspects

2.1 Siting These buildings are typically found in flat terrain. They do not share common walls with adjacent buildings. Sincethe major cities of Pakistan are located on flat terrain, it can be safely said that reinforced-concrete frame structures aremost commonly found in flat areas. However, after the October 2005 earthquake and the reconstruction following inits wake, reinforced-concrete buildings are constructed in the hilly areas of Abbottabad and Mansehra, too, but theirproportion in the total building stock is much less (not more than 1 to 2% of the total building stock) as compared tothe major cities. Small residential buildings located in densely populated areas of cities do not have an appreciable

distance between them but larger buildings do have a distance from 3 to 10 meters between them When separated

from adjacent buildings, the typical distance from a neighboring building is 3 to 10 meters.

2.2 Building Configuration Reinforced-concrete structures are usually rectangular in plan. However, in certain cases other planar profiles such as L,T, U or even curved profiles can also be found in larger buildings like plazas and hotels, aesthetics being the mainmotivation in adopting irregular shapes. In elevation, these buildings usually have a regular configuration; however, insome cases the difference in stiffness in different stories may cause soft story effect. In privately owned buildings, thetrend has been to allocate the ground and first floors to commercial facilities like shops while the upper stories are usedas residential dwellings in form of apartments. In order to increase the floor area, these apartments are projectedoutwards thus causing disproportion between the inter story stiffness. A typical building plan, elevation and picture ofconstruction are given in Figure 1, 2 and 3, respectively. The infills used in reinforced-concrete frames are usuallyconstructed in brick and block masonry. In residential facilities each room is normally provided with one or two doorsand one or two windows. Doors are usually located near the corners of the rooms with sizes in the range of 3.0 squaremeters and are usually wooden, but in some instances aluminum doors are constructed nowadays owing to theirdurability as compared to wooden doors. Windows are provided in the walls with sizes of 2.0 to 2.25 square meters.Reinforced-concrete lintels are provided above the openings in the brick masonry infills. These lintels are connected tothe columns by dowel bars in case of good quality construction but in ordinary construction, this feature is missing.When reinforced-concrete buildings are used to house commercial facilities, openings may be lesser and differentlylocated as compared to the ones in residential units though the sizes of the openings are almost the same. Infills inconcrete frames may be of different material for commercial buildings, usually glass infills for decorative purposeswhich are provided generally in the front walls. Such type of individual commercial units usually have one door and noopenings.

2.3 Functional Planning The main function of this building typology is mixed use (both commercial and residential use). Other use is for

public buildings like hospitals or schools etc. Reinforced-concrete structures are primarily used to accommodatecommercial and public facilities such as hotels, shopping malls, hospitals, schools etc. In the recent past, reinforced-concrete buildings have started to be used to accommodate residential apartments, too, while in some cases onebuilding may be used for both commercial and residential purposes. The number of apartments in a building wouldprimarily depend on the overall area of a particular building. Each of these apartments usually accommodates a singlefamily (on average consisting of four persons). In a typical building of this type, there are 1-2 elevators and no fire-

protected exit staircases. Access to the upper floors in reinforced-concrete buildings is provided through stairs or insome cases lifts. The number of stairways primarily depends on the area of the building. In the majority of reinforced-concrete buildings, there usually is no concept of provision of emergency escape routes so in case of any emergencythese stairs are the only means of escape from these buildings. Stairs have a width of 1.2 to 1.5 meters, however insome cases, smaller widths as low as 1 meter have been observed.

2.4 Modification to Building When modified, reinforced-concrete buildings are modified at times without permission of the governing authoritythat is responsible for the construction in a particular area and in some instances the builder may get away with it, too.The most common modifications performed on the building are relocation of the masonry infill walls to suit theneeds of the residents. In some cases, brick masonry infill walls are replaced with wooden boards as partition walls.Other modifications include the construction of additional stories as well as the confinement of the terraces to increaseliving space. The addition of stories that are not considered in the design of the building can lead to catastrophes.

Figure 1: Plan of a typical reinforced-concretebuilding in Pakistan.

Figure 2: Elevation of a typical reinforced-concretebuilding in Pakistan.

Figure 3: Construction of building in progress.

3. Structura l Deta ils

3.1 Structura l System Materia l Type of Load-Bearing Structure # Subtypes Most appropriate type

Masonry

Stone Masonry Walls

1Rubble stone (field stone) in mud/lime mortar or w ithout mortar (usually w ith timber roof)

☐

2 Dressed stone masonry (inlime/cement mortar) ☐

Adobe/ Earthen Walls

3 Mud w alls ☐4 Mud w alls w ith horizontal w ood elements ☐5 Adobe block w alls ☐6 Rammed earth/Pise construction ☐

Unreinforced masonryw alls

7 Brick masonry in mud/limemortar ☐

8 Brick masonry in mud/limemortar w ith vertical posts ☐

9 Brick masonry in lime/cementmortar ☐

10 Concrete block masonry incement mortar ☐

Confined masonry

11 Clay brick/tile masonry, w ithw ooden posts and beams ☐

12Clay brick masonry, w ithconcrete posts/tie columnsand beams

☐

13 Concrete blocks, tie columnsand beams ☐

Reinforced masonry

14 Stone masonry in cementmortar ☐

15 Clay brick masonry in cementmortar ☐

16 Concrete block masonry incement mortar ☐

17 Flat slab structure ☐

Structural concrete

Moment resistingframe

18 Designed for gravity loadsonly, w ith URM infill w alls

☐

19 Designed for seismic effects,w ith URM infill w alls ☑

20 Designed for seismic effects,w ith structural infill w alls ☐

21 Dual system – Frame w ithshear w all ☐

Structural w all22 Moment frame w ith in-situ

shear w alls ☐

23 Moment frame w ith precastshear w alls ☐

Precast concrete

24 Moment frame ☐25 Prestressed moment frame

w ith shear w alls ☐26 Large panel precast w alls ☐27 Shear w all structure w ith

w alls cast-in-situ ☐

28 Shear w all structure w ithprecast w all panel structure ☐

Steel

Moment-resistingframe

29 With brick masonry partitions ☐30 With cast in-situ concrete

w alls ☐31 With lightw eight partitions ☐

Braced frame32 Concentric connections in all

panels ☐

33 Eccentric connections in afew panels ☐

Structural w all34 Bolted plate ☐35 Welded plate ☐

Timber Load-bearing timberframe

36 Thatch ☐37 Walls w ith bamboo/reed mesh

and post (Wattle and Daub) ☐

38Masonry w ith horizontalbeams/planks at intermediatelevels

☐

39 Post and beam frame (nospecial connections) ☐

40 Wood frame (w ith specialconnections) ☐

41Stud-w all frame w ithplyw ood/gypsum boardsheathing

☐

42 Wooden panel w alls ☐

OtherSeismic protection systems

43 Building protected w ith base-isolation systems ☐44 Building protected w ith

seismic dampers ☐Hybrid systems 45 other (described below ) ☐

Reinforced-concrete buildings prior to the Kashmir 2005 earthquake were mostly designed for gravity loading only.However, after the Kashmir 2005 earthquake, a reasonable importance is being given to consideration of earthquakeinduced loading in the design of these buildings. Reinforced-concrete buildings in Pakistan at present are generallydesigned as moment-resisting frames, however, a particular building-resisting system would depend largely on thebudget allocated to the project and to some extent on the importance of the building. Low- to mid-rise buildings aregenerally OMRF, while taller buildings with a higher importance level, are designed as SMRF or dual systems(moment-resisting frame with shear walls).

3.2 Gravity Load-Resisting System The vertical load-resisting system is reinforced concrete moment resisting frame. Gravity loads are resisted purely bythe reinforced-concrete frame. The typical load transfer path is from the slabs to beams to columns and finally to the

footings of the building.

3.3 Latera l Load-Resisting System The lateral load-resisting system is reinforced concrete moment resisting frame. Different lateral load resistingsystems are provided by structural designers in the reinforced-concrete buildings in Pakistan. Reinforced-concreteframes usually are either OMRF or IMRF. Very important buildings have SMRF configuration as well as in some casesdual systems are encountered, too. Reinforced-concrete frames usually have brick or block masonry infill walls whichhelp contribute to the lateral load-resisting system.

3.4 Building Dimensions The typical plan dimensions of these buildings are: lengths between 10 and 40 meters, and widths between 10 and 20meters. The building has 3 to 8 storey(s). The typical span of the roofing/flooring system is 3 to 6 meters. Thetypical plan dimensions may be different than the mentioned spans depending on the nature of the building. In somecommercial buildings, spans as small as 3 meters have been observed. Construction joints are provided usually after 30meters in one direction if the building size is larger. Number of stories varies from city to city and building to building.In the less developed cities of Peshawar, Faisalabad and Quetta etc., reinforced-concrete buildings are low- to mid-rise(3 to 8 stories with a story height of about 3 meters). In the well-developed cities like Lahore and Islamabad,reinforced-concrete buildings are mid-to-high rise, usually 8 to 15 stories on average. Reinforced-concrete buildings inKarachi are usually high rise, an average number of stories being 15 and in many cases even taller (25 to 30stories). The typical storey height in such buildings is 3 meters. The typical structural wall density is none. .

3.5 Floor and Roof System

Materia l Description of floor/roof system Most appropriate floor Most appropriate roof

MasonryVaulted ☐ ☐Composite system of concrete joists andmasonry panels ☐ ☐

Structural concrete

Solid slabs (cast-in-place) ☑ ☑Waffle slabs (cast-in-place) ☐ ☐Flat slabs (cast-in-place) ☑ ☑Precast joist system ☐ ☐Hollow core slab (precast) ☐ ☐Solid slabs (precast) ☐ ☐Beams and planks (precast) w ith concretetopping (cast-in-situ) ☐ ☐Slabs (post-tensioned) ☐ ☐

Steel Composite steel deck w ith concrete slab(cast-in-situ) ☐ ☐

Timber

Rammed earth w ith ballast and concrete orplaster finishing ☐ ☐Wood planks or beams w ith ballast and concrete or plaster finishing ☐ ☐Thatched roof supported on w ood purlins ☐ ☐Wood shingle roof ☐ ☐Wood planks or beams that support clay tiles ☐ ☐Wood planks or beams supporting naturalstones slates ☐ ☐Wood planks or beams that support slate,metal, asbestos-cement or plastic corrugatedsheets or tiles

☐ ☐

Wood plank, plyw ood or manufactured w oodpanels on joists supported by beams or w alls ☐ ☐

Other Described below ☑ ☑

Floors/roofs are generally constructed in reinforced concrete and are monolithic with the load-resisting system(beams). Usually the thickness of roof slabs is 0.13 to 0.15 meters. Slabs are supported on their edges by beams which

are cast monolithical with reinforced-concrete slabs.

3.6 Foundation

Type Description Most appropriate type

Shallow foundation

Wall or column embedded insoil, w ithout footing ☐Rubble stone, fieldstoneisolated footing ☐Rubble stone, fieldstone stripfooting ☐Reinforced-concrete isolatedfooting ☑Reinforced-concrete stripfooting ☑Mat foundation ☑No foundation ☐

Deep foundation

Reinforced-concrete bearingpiles ☐Reinforced-concrete skinfriction piles ☑Steel bearing piles ☐Steel skin friction piles ☐Wood piles ☐Cast-in-place concrete piers ☐Caissons ☐

Other Described below ☐

It consists of reinforced concrete skin-friction piles. Foundations for low- to mid-rise reinforced-concrete buildingsare usually isolated column footings with size in the range of 1.5 square meters with thickness of about 0.15 meters. Alayer of lean concrete is usually provided beneath the footing to act as a cushion against the soil effects. At timescombined footings are also provided when loads are higher for low- to mid-rise buildings. In larger structures andheavy loadings, raft foundations are preferred in recent construction practice. In high-rise buildings, taller than 20stories, deep foundations are also provided consisting of usually skin-friction piles.

4. Socio-Economic Aspects

4.1 Number of H ousing Units and Inhabitants Each building typically has 21-50 housing unit(s). The number of housing units in a reinforced-concrete buildingprimarily depends on the size of the building and the function of the building (residential, commercial or publicbuilding). The usual number of housing units in an average sized reinforced-concrete building used for residentialpurposes is from 20 to 50. Reinforced-concrete buildings housing commercial facilities may have more commercialunits since they require relatively less space for their establishment. Generally, an average sized reinforced-concretebuilding may house 60 to 80 commercial facilities. On the other hand, public buildings in the form of reinforced-concrete buildings may have 40 to 50 offices located in them for an average sized building. The number of inhabitantsin a building during the day or business hours is more than 20. Depending on the nature of the building, thenumber of residents is highly variable. The total number of occupants during the day time tend to be lower ascompared to the occupants at night time. The number of inhabitants during the evening and night is more than20. As these types of structures are used for residential, commercial and public services, the number of residents inthese buildings may alter by quite an appreciable margin depending on the time of the day. The number of occupantsresiding in a residential multi-story reinforced-concrete building would depend on the size of the residential unit andthe number of residential units in that building. Usually 4 to 6 residents reside in one building unit and depending onthe size, the number of occupants in one building may reach in terms of hundreds. In reinforced-concrete buildingsaccommodating commercial and public facilities, there can be a higher variation in the number of people present in the

building at a given time due to the nature of the use. The inhabitants in these buildings may reach into hundredsduring the day while the number of occupants may trickle down to 5 to 10 residents during the night time.

4.2 Patterns of Occupancy As these types of structures are used for residential, commercial and public services, the number of residents in thesebuildings may alter by quite an appreciable margin depending on the time of the day. The number of occupantsresiding in a residential multi-story reinforced-concrete building would depend on the size of the residential unit andthe number of residential units in that building. Usually 4 to 6 residents reside in one building unit and depending onthe size, the number of occupants in one building may reach in terms of hundreds. In reinforced-concrete buildingsaccommodating commercial and public facilities, there can be a higher variation in the number of people present in thebuilding at a given time due to the nature of the use. The inhabitants in these buildings may reach into hundredsduring the day while the number of occupants may trickle down to 5 to 10 residents during the night time.

4.3 Economic Level of Inhabitants

Income class Most appropriate type

a) very low -income class (very poor) ☐b) low -income class (poor) ☐c) middle-income class ☑d) high-income class (rich) ☑

Reinforced-concrete frame structures, if used as residential buildings, are normally constructed in areas which give thebest access to the city center, hence the price of the single residential units are higher. However, due to the populationburst in the recent past, buildings are being constructed in the suburbs of the main cities, too. However, since thesebuildings are developed by well-established builders with a better quality of construction, the price tag of these units ishigh. Therefore, the cost of a single residential unit is highly variable, depending upon the location of the building, thequality of construction, the size of the housing unit and the story it is located (lower stories tend to be expensive).Commercial buildings are usually constructed in the city center or close to it, where the cost of land is highly inflated.For this reason the cost of building units in reinforced-concrete buildings in these areas is very high.

Ratio of housing unit price to annual income Most appropriate type

5:1 or w orse ☑4:1 ☐3:1 ☐1:1 or better ☐

What is a typica l source offinancing for bu ildings of thistype?

Most appropriate type

Ow ner financed ☑Personal savings ☑Informal netw ork: friends andrelatives ☐Small lending institutions / micro-finance institutions ☐Commercial banks/mortgages ☐Employers ☐Investment pools ☐Government-ow ned housing ☑Combination (explain below ) ☐other (explain below ) ☐

The most common source of financing for reinforced-concrete buildings is by the owner of the building whichmaybe private or government owned. In case of privately owned buildings, there may be multiple owners of thebuilding if the cost of construction is too high. Reinforced-concrete buildings housing residential units are usuallyconstructed by developers who subsequently either rent them out, or sell the individual housing units. In some cases,the builders would sell the individual units before they are constructed and use this capital to help construct thebuilding. Buildings housing commercial facilities have a similar pattern of financing. Public buildings (owned bygovernment of Pakistan) are owned and constructed by a government organization. In each housing unit, there are

no bathroom(s) without toilet(s), no toilet(s) only and 2 bathroom(s) including toilet(s).

It is normal in the architectural features of a building in Pakistan to provide a separate toilet with bathing facilities foreach bedroom in a residential unit. Since each unit of a residential building houses 1 to 3 bedrooms, the number ofbathrooms maybe 2 to 3. In reinforced-concrete buildings housing commercial facilities, there may be a collective toiletallocated to a particular number of commercial units or there may be toilets provided at each floor level for inhabitantsof that floor. .

4.4 Ownership The type of ownership or occupancy is renting, outright ownership , individual ownership and ownership by a groupor pool of persons.

Type of ownership oroccupancy? Most appropriate type

Renting ☑outright ow nership ☑Ow nership w ith debt (mortgageor other) ☐Individual ow nership ☑Ow nership by a group or pool ofpersons ☑Long-term lease ☐other (explain below ) ☐

The typical ownership is that either the owner of the building sells the ownership rights to the interested people or heputs out the individual housing units on rent. So these buildings are either owned by a single person or in manyinstances by multiple individuals who reside in these building units. The same pattern of ownership applies tobuildings housing commercial facilities. In case of public buildings, they are used primarily for government offices andin some instances maybe rented out to commercial facilities.

5. Seismic Vulnerability

5.1 Structura l and Architectura l Features Structura l/Architectura lFeature

StatementMost appropriate type

Yes No N/A

Lateral load path

The structure contains a complete load path for seismicforce effects from any horizontal direction that servesto transfer inertial forces from the building to thefoundation.

☑ ☐ ☐

BuildingConfiguration

The building is regular w ith regards to both the planand the elevation. ☐ ☑ ☐

Roof construction

The roof diaphragm is considered to be rigid and it isexpected that the roof structure w ill maintain itsintegrity, i.e. shape and form, during an earthquake ofintensity expected in this area.

☑ ☐ ☐

Floor construction

The floor diaphragm(s) are considered to be rigid and itis expected that the floor structure(s) w ill maintain itsintegrity during an earthquake of intensity expected inthis area.

☑ ☐ ☐

Foundationperformance

There is no evidence of excessive foundation movement(e.g. settlement) that w ould affect the integrity orperformance of the structure in an earthquake.

☑ ☐ ☐

Wall and framestructures-redundancy

The number of lines of w alls or frames in each principaldirection is greater than or equal to 2. ☑ ☐ ☐

Wall proportions

Height-to-thickness ratio of the shear w alls at each floor level is:

Less than 25 (concrete w alls);

Less than 30 (reinforced masonry w alls);

Less than 13 (unreinforced masonry w alls);

☑ ☐ ☐

Foundation-w allconnection

Vertical load-bearing elements (columns, w alls)are attached to the foundations; concretecolumns and w alls are dow eled into thefoundation.

☑ ☐ ☐

Wall-roofconnections

Exterior w alls are anchored for out-of-plane seismiceffects at each diaphragm level w ith metal anchors orstraps

☐ ☑ ☐

Wall openings

The total w idth of door and w indow openings in a w allis:

For brick masonry construction in cement mortar : lessthan ½ of the distance betw een the adjacent crossw alls;

For adobe masonry, stone masonry and brick masonryin mud mortar: less than 1/3 of the distance betw eenthe adjacent crossw alls;

For precast concrete w all structures: less than 3/4 ofthe length of a perimeter w all.

☐ ☐ ☑

Quality of building materialsQuality of building materials is considered to beadequate per the requirements of national codes andstandards (an estimate).

☐ ☑ ☐

Quality of w orkmanshipQuality of w orkmanship (based on visual inspection offew typical buildings) is considered to be good (perlocal construction standards).

☐ ☑ ☐

MaintenanceBuildings of this type are generally w ell maintained and thereare no visible signs of deterioration of buildingelements (concrete, steel, timber)

☐ ☑ ☐

Additional Comments

5.2 Seismic Features Structura lElement Seismic Deficiency Earthquake Resilient Features Earthquake Damage Patterns

Frame(columns,

beams)

Inadequate seismic design, sub-standard concretequality, disparity betw een the specified design andactual layout of reinforcement, deficiency in theprovision of clear cover in concrete, vertical

alignment of columns is sometimes not ensured.

Due to high redundancy, multipleload paths are available for efficientresistance of seismic forces, masonryinfill w alls contribute to the lateralresisting system.

Strong beam-w eak column failures are the mostcommon. In October 2005 Muzaffarabadearthquake, main failure w as due to theformation of the plastic hinges just below thebeam-column connection and at the base of the

column. Roof andfloors

The usual thickness of the roof slabsis 125 to 150 mm. These slabs havehigh stiffness and thus efficientlytransfer the seismic loads to theconcrete frames they are connectedto.

As such, failure of the roof slabs and floorsw ere not noticed in the Muzaffarabad 2005earthquake. The roof slabs that failed w ere dueto the additional demand that w as a result of

the failure of the adjoining frame elements. Foundations Seismic design of the isolated column footing is

not usually considered. Though rarely anyfoundation failure w ere observed in the October

In some cases, plinth beams areprovided to connect the individualspread footings. This practice results

As such no damage of the foundations w asobserved in reinforced concrete structures during

the past earthquakes in Pakistan.

2005 Muzaffarabad earthquake. in a more efficient seismicperformance of the RC frames.

During the past earthquakes, especially the Kashmir 2005 earthquake, almost all types of construction were heavilydamaged. Mostly damaged was the load-bearing brick masonry structures and stone masonry residential buildings.Reinforced-concrete buildings failed too in many places, especially the worst hit areas of Abbottabad and Mansehra andeven in the national capital, Islamabad. Deficiency in the construction materials (concrete, improper placement of thereinforcement etc.) and strong beam-weak column phenomena were the main reasons for the failure of the RC framestructures. These local failures caused global instability in the structural system. Typical damage patterns of reinforcedconcrete are given in Figures 4, 5 and 6.

5.3 Overall Seismic Vulnerability Rating The overall rating of the seismic vulnerability of the housing type is C: MEDIUM VULNERABILITY (i.e., moderateseismic performance), the lower bound (i.e., the worst possible) is B: MEDIUM-HIGH VULNERABILITY (i.e., poor

seismic performance), and the upper bound (i.e., the best possible) is D: MEDIUM-LOW VULNERABILITY (i.e.,

good seismic performance).

Vulnerability high medium-high medium medium-low low very low

very poor poor moderate good very good excellent

VulnerabilityClass

A B C D E F

☐ ☑ ☐ ☑ ☐ ☐

5.4 H istory of Past Earthquakes Date Epicenter, region Magnitude Max. Intensity

1994 Hindu Kush 6.5 V 2002 Hindu Kush 6.3 V 2005 Kashmir 7.6 VI-VIII

A low to moderate seismic activity has been active in many parts of Pakistan, especially in the Northwestern province,though the other parts of Pakistan had also experienced mild to severe intensity earthquakes in the past. In 1936, theearthquake with a magnitude of 8.1 on the Richter scale, that hit the capital of the Balochistan province, Quetta,resulted in a very high death toll (around 30,000 killed). But the usual seismic activity occurs in the northwestern partof Pakistan with the epicenter in range of 250 kilometers from the provincial metropolis, Peshawar. According toMSK, Peshawar may be placed in intensity zone VI or at most in VII, Islamabad in VI, and Lahore in V. In October2005, a strong earthquake hit the upper northern parts of the NWFP province causing severe damage to buildings andresulted in loss of lives in the tune of 70,000.

Figure 4: Typical damage pattern of strong beam-w eak column in 2005 Kashmir earthquake.

Figure 5: Total structural collapse of reinforced-concrete building in 2005 Kashmir earthquake.

Figure 6: Global instability of a reinforced-concretebuilding during Kashmir 2005 earthquake.

6. Construction

6.1 Building Materia ls

Structura lelement Bu ilding materia l Characteristic

strength Mix proportions/dimensions Comments

Walls

Usually unreinforced brickmasonry w alls are used inreinforced-concrete buildings,how ever, in some cities, likeKarachi, scarcity of bricks hasforced builders to use blockmasonry infill w alls. Masonryinfill w alls are laid usually incement-sand mortar.

Brick masonrycompressionstrength varies from2 to 5 MPa.

1:8 cement sand or 1:4: 4 cement, sand and stone dust. Brick size: 230mm x 115 mm x 65 mm. w alls are usually 230 mm thick how ever insome instances half brick w alls having thickness of 115 mm are alsoprovided as masonry infills.

Foundation Concrete and steel.

Concrete has acompressivestrength of 17 to 21MPa. Steelreinforcement has ayield strength of275 to 415 MPaand a tensilestrength of 480 to625 MPa.

Concrete mix proportions of 1:2:4 (Cement, Sand, Coarse aggregate) areused for construction of foundations. Foundations are usually isolatedcolumn footings having an average w idth of 1.5 square meters w ith athickness of 0.15 meters.

Frames(beams &columns)

Concrete and reinforcing steelare used for the constructionof frame elements.

Concrete has acompressivestrength of 17 to 21MPa. Yield strengthof steel is in therange of 275 to 415MPa and a tensilestrength from 480to 625 MPa.

A mix ratio generally used for concrete for the construction of frameelements is from 1:1.5:3 to 1:2:4, in w hich the former mix proportion attimes is used for construction of columns w hile the later is mostcommonly used for construction of beams. Size of the members w ouldprimarily depend on the structural configuration and the loading that thesystem is subjected to. How ever, the average size of beams is from 305mm and 460 mm (w idth and depth) to 380 mm and 760 mm.Columns are usually square w ith dimensions ranging from 305 mm x305 mm to 460 mm x 460 mm.

Roof andfloor(s)

Floors and Roofs are usuallyconstructed as reinforcedconcrete slabs w ith differentconfigurations. Materials usedfor construction are concreteand reinforcing steel.

Concrete has acompressivestrength of 17 to 21MPa. Yield strengthof steel is in therange of 275 to 415MPa and a tensilestrength from 480to 625 MPa.

Concrete has a compressive strength of 17 to 21 Mpa. Yield strength ofsteel is in the range of 275 to 415 MPa and a tensile strength from 480to 625 MPa. Floors and roofs are usually 150 mm thick on average.

6.2 Builder Regarding the residents of reinforced-concrete buildings in Pakistan, as stated earlier, these buildings are constructedeither by government, a single owner or a consortium. Government buildings are mostly used for housinggovernment offices, however in some cases these buildings may be used for dual purpose of accommodatinggovernment offices as well as some commercial facilities like shops or gathering halls etc. If these buildings areconstructed privately by a single owner, he would either sell the building units (commercial or residential) to interestedparties or may rent these out. Buildings constructed by conglomerates are usually sold to the users.

6.3 Construction Process, Problems and Phasing Construction process of reinforced concrete buildings may be different for public and privately owned buildings. Incase of public buildings, owned by government of Pakistan, the concerned line department both designs and supervisethe construction itself or it may hire services of a private consulting agency to carry out the design and supervise theexecution of construction activities. In case of privately owned reinforced concrete buildings, several possibilities havebeen observed. The owners may hire the services of an architect for carrying out the architectural design of the building.Architects would further hire services of a structural engineer to carry out the structural design. Usually execution ofconstruction is carried out through a contractor who may either charge the owner through a BOQ (Bill of Quantities)or carry out the construction by providing with skilled workmen while the materials are supplied either by a third partyor arranged by the owners themselves. The former procedure amongst the two is more common. The constructionsequence involves the leveling of the work site, excavation of the foundation pits, pouring of lean concrete (1:4:8 or

1:8:16), placement of the formwork and tying of the reinforcing bars and finally pouring of concrete. This is furtherfollowed up by the construction of the stub columns and plinth beams (in some cases) and the construction of thecolumns. Beams are cast in place after the construction of the columns making sure that there is enough embedmentof the column reinforcement into the beams. RCC slab follows the construction of the beams. Brick masonry infillwalls are constructed after laying of the roof slab and finally plastering and other finishing works are carried out. The

construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its

final constructed size. In well-planned construction, it is usually ensured that the actual construction would complyto the designed plans and structural configurations as provided by the design office. However, in some cases, thebuilders/owners may change the configuration of the building themselves. The usual changes incorporated in this wayare covering up open spaces to increase living area, relocation of infill walls etc.

6.4 Design and Construction Expertise Since a lot of capital is involved in the construction of reinforced-concrete buildings, the owners hire the services ofarchitects and structural engineers to carry out the architectural and structural design of the buildings. The expertise ofthese professionals varies from city to city in Pakistan. If a project is of high importance, architects and structuralengineers from other developed cities may also be employed for carrying out the designs. Regarding execution of theconstruction activities, in good projects, the contractor may hire services of a site engineer or a group of engineers forsupervising the construction activities, their number dependent on the spectrum of the project. Masons, steel fixersand other skilled workers rely solely on their experience gained over the years and are seldom trainedprofessionally. The role of engineers and architects for designing and construction of a reinforced-concrete building inPakistan vary from project to project and from city to city. For projects of importance, it has been a usual practice tohire services of an architect for carrying out the architectural design while a structural designer would further design theagreed architecture of the building. In construction, there may be or may not be site engineers hired for supervising theconstruction.

6.5 Building Codes and Standards This construction type is addressed by the codes/standards of the country. Building Code of Pakistan governs the

design and construction of reinforced-concrete buildings in Pakistan. The year the first code/standard addressing this

type of construction issued was 2007. Building code of Pakistan 2007 (BCP 2007) is the code that is followed fordesign of reinforced-concrete buildings. However, since BCP 2007 is essentially UBC 97 except for seismic zonationthat has been carried out indigenously, in true essence these buildings are designed in accordance with designspecifications of UBC 97. The specifications usually referred to regarding materials are ASTM specifications whichgovern the quality assurance of steel, concrete, bricks etc. The most recent code/standard addressing this construction

type issued was 2007. Building Code of Pakistan is typically used to design and construct these buildings.

Ideally the design and construction of reinforced concrete buildings should be governed by the building code ofPakistan. Every city has a building control authority that authorizes the construction after evaluating it. However thisevaluation in most cases is limited to verification of the proposed design in light of the local building by-laws. Inbuildings of high importance, there has been a growing trend in the major cities of Karachi and Lahore to vet thestructural designs too, though this practice is not common in the other cities. In government owned buildings,construction is either supervised by the nominated consultants or by the government organization itself whichsomehow ensures construction according to approved designs and specifications. On the other side, construction ofreinforced concrete buildings owned privately, there usually is no supervision of construction quality by a building codeenforcing agency. Summarizing it, it may be stated that designs are usually compliant to the building code of Pakistanwhile quality of construction vary and may not conform to the standard specifications.

6.6 Building Permits and Development Control Rules This type of construction is an engineered, and authorized as per development control rules.

Since reinforced-concrete buildings are mostly constructed in the urban areas of Pakistan which usually has a buildingcontrol authority that governs the construction of buildings in that particular city. Therefore building permits arerequired to execute construction of these buildings. Building permits are required to build this housing type.

6.7 Building Maintenance Typically, the building of this housing type is maintained by Owner(s) and Tenant(s). Since these buildings are either

sold to individual owners or rented out to tenants, maintenance of these buildings is carried out by either of these.

6.8 Construction Economics Unit construction cost of reinforced concrete buildings in Pakistan is highly variable. The cost varies according to thelocation of the building to the amount of facilities provided in the building. 10-15 persons working 8 hours a day

can complete an approximately 280 square meter building in four months.

Figure 7: Manual batching of concrete may result inmix proportions different than the specified

proportions.

Figure 8: Use of sub-standard formw orks result inconcrete dimensions different than the designed

dimensions.

Figure 9: Stomping of laborers over thereinforcement change its configuration thus

hampering its intended function.

Figure 10: Lack of provision of seismic hooksdespite follow ing the SMRF configuration may

result in performance much low er than designedone.

7. Insurance

Earthquake insurance for this construction type is typically unavailable. For seismically strengthened existingbuildings or new buildings incorporating seismically resilient features, an insurance premium discount or morecomplete coverage is unavailable. Earthquake insurance is not available in Pakistan. In some instances, it may be

available but building owners do not avail this facility.

8. Strengthening

8.1 Description of Seismic Strengthening Provisions

Strengthening of Existing Construction :

Seismic Deficiency Description of Seismic Strengthening provisions used

Strong beam-w eak column phenomenon CFRP jacketing w as carried out on the columns to strengthen them (Figure 11) Resizing of existing columns Column sizes w ere increased to incorporate additional capacity into the system (Figure 12)

Seismic strengthening is usually carried out in accordance with the Building Code of Pakistan.

8.2 Seismic Strengthening Adopted

Has seismic strengthening described in the above table been performed in design and construction practice, and if so,to what extent? Pakistan has been struck by many earthquakes ranging from mild to high intensities but there have been no records ofthe damages incurred by the buildings. The practice of retrofitting or strengthening has not been prevalent in Pakistan.People prefer to raze down the buildings and reconstruct them. This can be attributed to lack of research and absenceof skilled engineers working in the field of seismic retrofitting and strengthening. However, in recent times, especiallyin the areas severely affected by the 2005 earthquake, several projects have been carried out to retrofit schools andhospital buildings, but on a larger scale usually no retrofitting is carried out.

Was the work done as a mitigation effort on an undamaged building, or as repair following an earthquake? This work was carried out as a repair work after the Kashmir 2005 earthquake.

8.3 Construction and Performance of Seismic Strengthening

Who performed the construction seismic retrofit measures: a contractor, or owner/user? Was an architect or engineerinvolved? Strengthening was carried out by structural engineers from Earthquake Engineering Centre, University of Engineering& Technology, Peshawar.

What was the performance of retrofitted buildings of this type in subsequent earthquakes? There has been no earthquake of appreciable damage potential since this work was carried out to assess theperformance of the strengthened building.

Figure 11: CFRP jacketing is used in some buildings to strengthen the

existing columns.

Figure 12: Resizing (w idening) of the columns are carried out to increase

the potential of the structural system.

Reference(s)1. A critical review of the seismic risk zoning and development of design spectra for Peshawar and adjoining areas

Qaisar Ali and Akhtar Naeem Khan13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada 2004

2. Seismic performance study of brick masonry building systems in Peshawar region

Qaisar Ali

3. Observed Seismic Behavior of Buildings in Northern Pakistan During the 2005 Kashmir EarthquakeAmjad Naseer, Akhtar Naeem Khan, Zakir Hussain, and Qaisar AliEarthquake Spectra 2010 26

Author(s)1. Yasir Irfan Badrashi

Assistant Professor, Earthquake Engineering Centre, University of Engineering & Technology, Peshaw ar , PAKISTANEmail:yasir_badrashi@yahoo.com FAX: +92-91-9218223

2. Qaisar AliAssociate Professor, Department of Civil Engineering, NWFP University of Engineering and Technology Pesh, Peshaw ar 25000, PAKISTANEmail:engrqaisarali@yahoo.com FAX: -9217977

3. Mohammad AshrafAssistant Professor, Department of Civil Engineering, University of Engineering & Technology, Peshaw ar , PAKISTANEmail:engineerashraf@yahoo.com FAX: +92-91-9218223

Reviewer(s)1. Dominik Lang

Dr.-Ing., NORSARKjeller 2027, NORWAYEmail:dominik@norsar.no FAX: +47-63818719

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